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bcachefs: btree_and_journal_iter: don't iterate over too many whiteouts when prefetching

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To help ameloriate issues with peek operations having to skip over
deletions in the journal - just bail out if all we're doing is
prefetching btree nodes.

Since btree node prefetching runs every time we iterate to a new node,
and has to sequentially scan ahead, this avoids another O(n^2).

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2024-11-17 14:39:46 -05:00
parent 1d1374a083
commit 1a8f5adc20
3 changed files with 10 additions and 0 deletions
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2
fs/bcachefs/btree_iter.c
View File

@ -825,6 +825,8 @@ static int btree_path_prefetch_j(struct btree_trans *trans, struct btree_path *p
bch2_bkey_buf_init(&tmp);
jiter->fail_if_too_many_whiteouts = true;
while (nr-- && !ret) {
if (!bch2_btree_node_relock(trans, path, path->level))
break;

7
fs/bcachefs/btree_journal_iter.c
View File

@ -426,6 +426,7 @@ static void btree_and_journal_iter_prefetch(struct btree_and_journal_iter *_iter
: (level > 1 ? 1 : 16);
iter.prefetch = false;
iter.fail_if_too_many_whiteouts = true;
bch2_bkey_buf_init(&tmp);
while (nr--) {
@ -444,6 +445,7 @@ static void btree_and_journal_iter_prefetch(struct btree_and_journal_iter *_iter
struct bkey_s_c bch2_btree_and_journal_iter_peek(struct btree_and_journal_iter *iter)
{
struct bkey_s_c btree_k, journal_k = bkey_s_c_null, ret;
size_t iters = 0;
if (iter->prefetch && iter->journal.level)
btree_and_journal_iter_prefetch(iter);
@ -451,6 +453,11 @@ struct bkey_s_c bch2_btree_and_journal_iter_peek(struct btree_and_journal_iter *
if (iter->at_end)
return bkey_s_c_null;
iters++;
if (iters > 20 && iter->fail_if_too_many_whiteouts)
return bkey_s_c_null;
while ((btree_k = bch2_journal_iter_peek_btree(iter)).k &&
bpos_lt(btree_k.k->p, iter->pos))
bch2_journal_iter_advance_btree(iter);

1
fs/bcachefs/btree_journal_iter.h
View File

@ -26,6 +26,7 @@ struct btree_and_journal_iter {
struct bpos pos;
bool at_end;
bool prefetch;
bool fail_if_too_many_whiteouts;
};
static inline int __journal_key_btree_cmp(enum btree_id l_btree_id,